Signaling apparatus



Nov. 3, 1925.

S IGNALING APPARATUS Filed March 30. 1922 2 Sheets-Sheet l Nov. 3 1925.

E. B. CRAFT SIGNALING APPARATUS Filed March 30. 1922 2 Sheets-Sheet 2 'W MMILM Patented Nov. 3, 1925 UNITED STATES" PATEN T OFFICE.

EDWARD B. CRAFT, OF HACKENSACK, NEW JERSEY, ASSIGN OR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A

CORPORATION OF NEW YORK.

. s SIGNALING APPARATUS.

Application filed March 30, 1922. Serial No. 548,214.

To all whom it may concern:

Be it known that I, EDWARD B. CRAFT, a citizen of the United States, residing at l a .-kensaek, in the county of Bergen, State of New Jersey, have invented certain new and useful ln'iprovelnents in Signaling Apparatus, of which the following is a full, clear, concise. and exact description.

. This invention relates to signaling systems and apparatus, and particularly to a unitary equipment comprising a phonograph and a signaling-receiving svstem,-capable of translating. into sound either signals locally reproduced from a sound record. or signals such as high frequency signals received from a distant station.

An object of the invention is to provide means for actuating a loud speaking horn orreceiver either by signals received from a distant point, such as speech frequency, vcarrier or radio signals, or by signals locally reproduced from .a phonograph sound record. v

Another object of the invention is to proride amplifying means associated with the loud speaking receiver for amplifying both signals transmitted from a distance and the signals from the phonograph reproducer.

Another object is to provide a phonograph reproducer. high frequency receiving system, and a loud speaking receiver, all energized from the same source of energy.

Other objects will hereinafter appear.

The above-mentioned equipment, including the signal receiving system, the electric flronograph reproducer, the amplifying means, and the loud speaking receiver, are n'eferably arranged in a compact box or cabinet, one side of which may constitute a control panel on which the necessary control switches may be mounted. The source of energy, which may be a motor generator set. rectifier, or' storage batteries, may also be nlouutedwithin the same box. Switching means is provided so'that the operator may readily connect the loud-speakingreceiver either with the signal receiving system or with the phonograph reproducer;

leferring to the drawings. i

1 represents the circuit of one embod iment of this invention in which the signal receiving system is adapted 'to receive radio signals;

Fig. 2 illustrates a cabinet whichvmay have mounted therein the apparatus schematically illustrated in Fig. 1;

.l ig. 3 is a cross section of the cabinet of Fig. 2, taken along the line marked 33.

Referring to Fig. 1. the circuit disclosed therein comprises a high frequency receiving system A and an electric phonograph reproducer B. each of which may be electrically connected at will, to a loud speaking receiver C.

The high frequency receiving system A comprises a high frequency receiving conductor, such as an antenna 6, which is serially connected with an adjustable condenser 7 and the primary winding 8 of a transformer 9, the coupling of which is adjusta ile. The secondary winding 10 of the transformer is connected to the input terminals of a high frequency detector 11 which may, for example, be a vacuum tube of the three-electrode type, the operation of which is now well known in the art. Connected in shunt to winding 10 is an adjustable condenser 13 which may be adjusted for the well-known purpose of tuning the secondary winding circuit to the high frequency it is desired to receive. The low frequency currents present in the output circuit of detector 11 are impressed by a transformer 14 upon the inputwircuit of an amplifier 15 which, for example, may be a vacuum tube amplifier of the three-electrode type. \Vhen the double-pole, double-throw switch 17 is thrown to the left to make connection with contacts 18 and 19, the amplified low frequency currents from tube 15 are impressed through transformer 20 upon the input .circuit of a second vacuum tube amplifier 22 and are thereby amplified to a still greater degree before being translated into sound waves by the loud speaking receiver 23. which is connected in the output circuit of amplifier 22. VVitb such-an arrangement the antenna 6 and the secondary circuitassociated therewith may be tuned to receive signals of a radio frequency modulated in accordance with low frequenc'ysig nals. The modulated waves will be detected by the vacuum tube detector 11 and the resulting low frequency signals will be amplified. to any desired degree by amplifiers 15 and 22 andtranslated into sound the loud speaking receiver 23. The amount of amplification may be regulated by varying the setting of the potentiometer 24 which is shown connected in shunt waves by to the secondary winding of transformer- 20. The adjustable tap of the potentiometer is connected to the control electrode of amplifier 22. i

It will be frequently desirable to effectively shunt the primary winding of transformer 14 by a condenser 25 which has a low impeden'ce to currents of high frequency such as the frequencies received by antenna 6, but which offers very high impedance to speech frequencies. Condenser 25 will then serve to shunt out any high frequency ing in either direction. The total value of works into its own impedance.

resistance 24, all of which is in circuit with the secondary Winding of transformer 20, should have such a value that amplifier 15 desirable for good quality transmission, that the impedance of receiver 23 should be such that the external impedance between the anode and cathode of tube 22 is of the same order of magnitude as the internal im- .pedance between the anode and cathode.

In order to supplyv space current for tubes 11, 15 and 22, and-to heattheir filaments 28, 29, and 30, a motor generator set D may be rovided. This set, as shown in the drawing, comprises an alternating current motor 31, which, when a double-pole, double-throw switch 32 is thrown in either direction, is energized by current from leads 33 connected, for example, to terminals of an ordinary 110 volt power line. Secured to thesame shaft as the motor 31 is a direct current generator having a high voltage shunt field winding 34 and a low voltage shunt field winding 35. The low voltage brushes 36 and 37 are connected in circuit with the three filaments by a path whichincludes conductor 38-,filament 30, switch blade 39v of switch 17 filaments 29 and 28, adjustable resistance 40 and conductor 41. The voltage delivered by the low voltage brushes ofthe generator will depend, of course, upon the number of filaments to Connected effectively in shunt to the hig '1 volitage' brushes 42 and 43 of the generator,

the low It is also be supplied by current therefrom. In the case illustrated, em I ploying only is a potentiometer 45, the adjustable contact of which is connected to the anode 46 of tube 11 while the fixed terminal of the potentiometer is connected to the corresponding cathode 28. This enables the anodecathode voltage of the detector tube 11 to be readily adjusted to any desired value. Since in general it may be found desirable to employ as amplifiers, tubes requiring higher anode-cathode voltage than is necessary for the detector tube, practically the entire potential drop across the resistance 45 may be impressed upon the output circuits of tubes 15 and 22. The cathode 29 is connected to the negative side of potentiometer a connection which includes cathode 28 and adjustable resistance 40. The anode of tube 15 is connected to the positive side of resistance 45 by connection including the primary vwinding of transformer 20. Similarly, cathode 30 of tube 22, is connected to the negative side of resistance 45 by a connection including switch blade 39, cathodes 29 and 28, and resistance 40, while the anode of tube 22 is connected to the posi- 'tive side of resistance 45 by a connection in.-

eluding loud-speaking receiver 23 and conductor 50.

If it is desired to make the detector grid 51 negative. with respect to its cathode 28, a

an adjustable resistance 40' common to the grid circuit and the filament heating circuit maybe provided. This Will make grid 51, negative with respect to filament 28 an amount equal to the IR drop across this resistance. This arrangement avoids the necessity of employing a separate primary source of voltage for obtaining the desired negative grid potential. Since grid 52 of tube 15 is connected to its cathode 29 through the secondary winding of transformer 14, resistance 40, and cathode 28, it follows that grid 52 is negative with respect to its filafilaments 28 and 29, since these filaments and the resistance 40 are connected between the grid of tube 22 and itscathode; This arrangement of having a greater negative grid potential on the last stages of a multi-stage amplifier set istoprevent the amplifier tubes from being overloaded and will also prevent distortion in the si als which sometimes occurs when the gri of an amplifying tube becomes too positive with respect to'its filament. It thus has been shown that the motor generator set D may be utilized for heating the filaments of the tubes, for supplying.

" ofl'er negligible the necessary space current, for producing the necessary potential difference between the grid and cathode of each tube, and for energizing the loud speaking receiver.

If desired, a filter may be provided in circuit with both the high voltage and low voltage brushes of the generator to filter out commutator noises and other alternating currents which would otherwise be impressed upon the tubes and reproduced by the loud-speaking receiver. Thus, between the filaments and the low voltage brushes is an electric wave filter of one section comprising two series inductances 53 and 54 and a shunt capacity 55, while between the high voltage brushes and the tubes is located a similar wave filter comprising series inductances 56 and 57, and a shunt capacity 58. As described in the United States Patent to Campbell, No. 1,227,113, of May 22, 1917, on electric wave filters, these inductances and capacities may be given such values as to substantially entirely suppress all frequencies above any desired value and in this particular case they should be designed to translate only direct current. That is, the inductances should be solarge as to otter a very high impedance to alternating currents, while the capacities should be so large as to impedance to alternating currents.

The arrangement described above has shown how the loud speaking receiver 23 may be energized by high frequency signals which have been detected and amplified/ If, however, the double-throw switch 17 is thrown to the right so as to make connection with contacts 60 and 61, the amplifier 22 and the loud speaking receiver 23 are disconnected from the high-frequency receiving system and are connected instead -to the electric phonograph reproducer B.

This phonograph reproducer comprises, in the form shown, two carbon button microphones 62 and 63 connected in push-pull relation and arranged in conjunction with a stylus holder 64. Energizing current for the carbon buttons is obtained from the low voltage brushes 36 and37 by connections which may be traced from low voltage brush 36 through inductances 53 and 54, conductor 38, filament 30, switch blade 39,

contact 61, resistance 65,-in parallel through the two halves of the primary windingof transformer 66 to the two carbon buttons 62 and 63, thence through conductors 67, 68,

and 41 to the other-low'voltage brush 37.

It will be notedthat the two filaments of the first two tubes 11 and 15 are no longer in circuit with the 'low voltage brushes. 'In order that the filament 30 of tube 22 may receive the same current as it did with filaments'28 and 29 also in circuit, and still a shunt resistance 69 are inserted in the supply leads and are given the proper values to insure the proper operation of the amplifier 22 and the electric phonograph reproducer 13.. The alternating current developed by the phonograph reproducer' is prevented from passing through the direct current leads to the generator by connecting effectively in shunt to these leads, a condenser-7O which has a low impedance to alternating currents of the frequencies generated by the phonograph reproducer. The alternating current generated by the reproducer and flowing through the primary winding of transformer 66 is impressed by means of switch 17 and potentiometer 24 upon the input terminals of amplifier 22 where the currents from the phonograph reproducer are amplified to any desired degree and impressed upon the loud speaking receiver 23. The setting of potentiometer 24. may be adjusted to vary the amplification produced by tube In some cases it may be found desirable to include such a small fraction of resistance 21 betweenthe grid and cathode of tube 22 that the eti'ectivc amplification produced by tube 22 is less instead of greater than unity, that is, the strength of the currents impressed on the loud-speaking receiver would then be less than the strength of the currents generated by the reproducer B; 1

It thus will be seen that when the switch 17 is thrown to the left to make connection -with contacts 18 and 19 that the loud speakingreceiver translates into sound waves the signals received by antenna 6, while the throwing of switch 17 to the right to make connection with contacts 60 and 61 causes the same loud speaking receiver to be en ergized by currents generated by the phonograph reproducer B.

The system just described should be designed so as to operate with the minimum amount of distortion. In particular the amplifiers, the loud speaking receiver, and the phonograph reproducer should be so designed as to be substantially distortionless. The preferred way to operate a vacuum tube amplifier without distortion is disclosed in the Arnold United States Patent No. 1,349,252, issued August 10. 1920. Forms of loud speaking receivers and phonograph reproducers which may be employed are shown respectively in Egerton vUnited States PatentlNo. 1,365,898 of January 18. 1921, and Egerton United States Patent No. 1,246,895 of November 20, 1917. These forms, however, are mentioned merely for illustrative purposes and are not intended to limit the lnvention in any way whatsoever.

One manner in which the apparatus, schematically illustrated in Fig. 1, may be compactly and conveniently mounted, is to employ a cabinet of the type now ordinarily employed in connection with the presentday phonograph. Such a cabinet 75 is illustrated. in Figs. 2 and 3.

In the lower part of the cabinet 7 may be mounted a control panel 7 6 on which are mounted various control elements of the system. Knobs 7 7, 78-, and 79 may be provided, for eXample,-to vary the adjustments of condensers 7 and13 and the coupling of transformer 9. The vacuum tubes 11, 15,

and 22 may also be supported by the panel so as to be available for observation purposes and ready replacement. Knobs 80, 81,

' 82, and 87 maybe employed to vary respectively the values of resistances 24, 10, 45,

' and 69, whenever in the operation of the system it may be found necessary to vary their values. i

The motor generator set shown in the back of the control panel is preferably resliently supported by a plurality of coiled springs 83 and 84, for example, and others not shown in the cross-sectional view, in order that the incidental vibration of the motor generator and its operation will not cause the whole cabinet to vibrate and thereby afi'ect the quality of the signals transmittedinto sound by the loud-speaking receiver. .-It is obvious that other means for resiliently mounting the motor generator mtiy be provided.

nthe upper part of'the cabinet may be mounted the usual rotatable plate or turn .such as a spring motor 90, although any other source of power may be employed.-

The horn attachment 91 associated with the loud-speaking receiver 23 may be of any desired configuration to insure good quality rendition.

If desired. the switches 32 and 17, which are employed respectively'for connecting the motor generator set to a power line and for connecting the loud-speaking receiver either to receive radio signals or signals from the phonograph reproducer, may be combined so that they may be controlled by a common actuating member 9.3, which, as shown in Fig. 3, is preferably mounted in the upper part of the cabinet in order to make it readily accessible when it is desired to change from one type of signal to the other. With such an arrangement, to transfer from one type of signal to the other, it is merely necessary to throw a single switch, thereby requiring the least amount of attention from the operator-when a changein the type of signal is desired.

Only-four connections external to the cabinet are needed in the form specifically illustrated. Two of the connections may be incorporated in a cable 94 leading to an ordinary electric light socket, for example, for obtaining the voltage supply for the motor generator, while conductors 95 and 96 may lead respectively to the high frequency receiving conductor and the ground connection.

I The antenna-employed in connection with the high frequency receiving system may be of any desired form, such as a loop antenna or an ordinary straight aerial. It is also coi'itemplated that in some cases it may be found desirable to employ a' loop antenna that is supported by the cabinet itself either externally or internally. In this latter case theekternal connection 95 would be unnecessary.

It is furthermore, contemplated that the high frequency receiving conductor 6 need not be an antenna of a radio system, but may be a slgnahng llne such as a telephone line upon which are impressed carrier cur- 1 rents modulated by low frequency signals. In other words, the system illustrated in the drawings is adapted to receive either high frequency carrier current signals or radio signals and translate each into audible sounds. It is also to be understood that the receiving conductor 6 may be a telephone line containing speech frequency signals to be impressed on the loud speaking receiver.

In the latter case the detector 11 is not necessary,'as the speech frequency signals could be impressed directly upon amplifier 15.

While a vacuum tube detector and vacuum tube amplifiers have been illustrated in the drawings and are preferable because they can be made to operate practically without distortion, it is to be understood that other typesof detectors and amplifiers may be employed, as this invention in its broader aspects is not limited to the use f electric discharge devices for .ampllfication or detection. It is, furthermore, to'be understood that as many stages of ampl fication as are desired may be employed either for the amplification of the signals from a distance or for those locally produced from a sound record.

It is also to be undertsood that the invention described above may be variously mod1.- fied from the specific form illustrated 1n the drawings without departing in any wise from the spirit of this invention as defined in the appended .claims. For example, while the cabinet illustrated is of the SO: called upright type, other forms may be found desirable particularly if greater separation is desired between the amplifiers and the power equipment. While an electric reproducer has been illustrated for v causing the loud-speaking born to emit sounds corresponding .to a. sound record, it

ultra-audio frequencysignals, an amplifier common to said reproducer and said rece1v-- ing setand switching'mechanism for causing said ampllifier to be operated at times by"detected other times to be operated by signals from said reproducer forefiecting the operation of said loud speaking receiver. i 2. A cabinet containing a loud speaking receiver, a high frequency receiving set, an electric phonograph reproducer, a common source of voltage for energizing said receiver, said receiving set, and said repro- 2 ducer, and connections for making. said receiver responsive at times to signals received a by said set and at other times responsive to signals produced by said-reproduce'r. V

3. A cabinet containing a loud speaking receiver, means for receiving highfrequency' signals and translating them into low fre'- quency signals, an electric phonograph reproducer, a source-oi voltage, and switch.-

ng mechanism which in one 'osition connects said receiving means wlth said loud speaking receiver and energizes-said receiving means and said receiver from said source of voltage. and in a second position connects said phonograph reiproduceri-to said 3 loud speaking recelver an ner izes said feproducer from said source'of vcfitage.

4.4 cabinet comprisin ahigh frequency "detector-of thevacuum tu e type, a vacuum tube amplifier, input circuit and an output circuit, and aving a cathode, an andde, and a trode, a loud speaking'receiver associated gh frequency signals and at :tector having a cathode, a vacuum tube am- 5 said detector and for removing the cathode 65 connections and for connecting the inp t 'c1r circuit connections.-

horn, electric devices inc y tube detector and a vacuum tu e'amplifier' 75' sounds reproduced from a sound record, 7 a unitarysource of .power for all of said, each of said tubes havin an mountedv control elecmeans for connecting the in ut circuit of saidamplifier at times with t e output circuit of said detector and at other times with said electric phonograph reproducer, and a source of volta e for energizing said detector, said amplifier, and said receiver when said detector is associated with said amplifier and for energizing said reproducer, said am lifier,.and said receiver when said ampli er is associated with said reproducer.

5. In combination, a "vacuum tube deplifier, having a cathode and having its input circuit associated with saiddetector, a

phonograph reproducer, a source of volta e, or-

ci'rcuit connections from said source heating said cathodes, means for disconnecting theinput circult. of said amplifier from of said detector from said heating ircuit cuit of said amplifier-to said reproducer, and

means in circuit with saidtreproducer .to

compensate for the" disconnection of the cathode of said detectorfrom'the heating-70 6. A cabinet comprisin a loud speaking udin a vacuum for causing said horn to emit sounds carried' by high frequency oscillations to said cabinet from a distant station,'devices in?- eluding an electrical reproducer forlcausing said horn to. emitlsounds corresponding to devices,=anda control panel ha' thereon means for controlling said "devices-i} I111 witnesswhe'reof, I hereunto subscribe .my name this'28th da' of March-A. -D., 1922. with the output circuit of said amplifie v:

.JED A 121) cRaFT f 

